The present invention generally relates to overspeed protection of sensorless electric drives and, more particularly, to apparatus and methods using software and hardware to achieve overspeed protection of sensorless electric drives.
The power electronics for aerospace applications play a significant role in the modern aircraft and spacecraft industry. This is particularly true in the area of more electric architecture (MEA) for aircraft and military ground vehicles.
The commercial aircraft industry is moving towards non-bleed air environmental control systems (ECS), variable-frequency (VF) power distribution systems, and electrical actuation. Typical examples are the latest designs, such as the Boeing 787 and the Airbus super jumbo A380. The next-generation Boeing airplane (replacement of 737) and the Airbus airplane (replacement for the A320) will most likely use MEA.
Some military aircraft already utilize MEA, including primary and secondary flight control. Military ground vehicles have migrated toward hybrid electric technology where the main power generation and propulsion employs electric machinery and associated power electronics. Therefore, substantial demand for high-performance electric drives has arisen.
High speed rotating machinery for aerospace applications is the core hardware for achieving high performance power generation and environmental control. The overspeed protection of this machinery is a very important feature to assure a fail safe operation. The pneumatic and hydraulic drives are typically designed to sustain overspeed operation of up to 50% exceeding the maximum normal operation. This requirement leads to substantial penalty in weight and volume. With implementing high speed electric drives there is a prospect of reducing this overspeed design requirements down to 7%. This opportunuity results from the ability of the modern electric drives to control the speed precisely. The accurate speed control is based on closed loop algorithms using shaft position sensors for speed measurement. However, there is a tendency to eliminate the shaft position sensors for increased reliability and reduced cost. Therefore, the real speed measurement in the most advanced sensorless control schemes does not exist.
Electric drives based on synchronous permanent-magnet machines may provide the best performance for high-speed aerospace applications. The torque in the synchronous machine may be produced by applying three-phase sinusoidal currents that create the stator flux. This stator flux may interact with the rotor flux created by a permanent magnet in such a way that they are locked to each other. Therefore, the rotating speed of the rotor may be synchronized with the excitation current of the stator. Based on this fundamental principal of operation, it is believed that as long as the excitation current of the machine controller does not exceed the maximum allowable mechanical frequency, the real speed of the drive will be within the required limit. This may be true during steady-state operation. However, there are some transient conditions in which the speed may experience overshoot above desired levels.
As can be seen, there is a need for improved apparatus and methods for overspeed protection for sensorless electric drives having improved performance and reduced cost. Such an overspeed protection methods should also result in reduced weight and volume.